A fine pattern of a semiconductor is formed by projecting, with reduction in size, a pattern etched on a photomask that serves like a negative of photography, or by using, like a stamp, a nano-imprint template on which a pattern of the same size is etched. In such a forming process, a defect inspection of a pattern, which serves as the original of the semiconductor, is very important.
In a general defect inspection device, telecentric optical systems and collimated optical systems are alternately arranged, and light is radiated on an inspection sample by an objective lens.
Here, if a maximum incidence angle of light rays to the inspection sample is expressed by θ and the refractive index of an image formation space is expressed by n, an NA of the optical system, that is, a numerical aperture, is defined as n sin θ. However, since the image formation space is usually in the air, n=1 and NA is expressed by sin θ. In addition, if the numerical aperture of illumination light is expressed by NA1 and the numerical aperture of the objective lens is expressed by NA2, the ratio NA1/NA2 thereof is called an illumination σ.